Compacting work machines are widely used in the construction and landscaping industries for the compaction of granular materials. Compacting machines come in a variety of forms including vibratory rammers, vibratory plate compactors and vibratory roller (or drum) compactors. This disclosure is directed to vibratory roller compactors, which are also referred to as rollers, articulated rollers, vibratory soil compactors, vibratory asphalt compactors and the term that will be used herein, utility compactors. Applications for such utility compactors include the compaction of sand, gravel, or crushed aggregate for foundations, footings, or driveways; base preparation for concrete slabs, asphalt parking lots, etc. Utility compactors are also used for the compaction of either hot or cold mix asphalt during patching or repairing of streets, highways, sidewalks, parking lots, etc.
The typical utility compactor includes one or two rollers or rollers that perform the actual compacting operation. The rollers are mounted to a main frame that supports an engine and associated equipment. An eccentric shaft, commonly known as an exciter, is located within and rotatably coupled to the roller by a second hydraulic motor. In hot mix asphalt compaction applications, the machine may be provided with a water tank and associated equipment for spraying water on the surface immediately in front of the roller to prevent the asphalt from congealing on the roller.
Utility compactors on the market today exhibit a number of drawbacks and disadvantages. First, the eccentric shaft used to vibrate the roller is very heavy, thereby increasing both manufacturing and operating costs. As shown in FIG. 1, a typical eccentric shaft 5 includes a straight bar 6 extending from one end 7 of the bar 6 to the other end 8, with eccentric weights 9 either press-mounted to, or cast with, the straight bar 6. Both press-fitting weights 9 eccentrically on a straight bar 6 or casting eccentric weights 9 with the straight bar 6 are costly manufacturing practices which, if replaced, could produce substantial cost savings. The current eccentric shaft designs are also heavy and therefore costly to manufacture. For example, for a roller that is 1 m wide, the shaft 5 of FIG. 1 weighs about 26.2 kg and has a first moment of inertia of about 0.24 kg·m and a second moment of inertia (a.k.a. mass moment of inertia) of about 0.034 kg·m2. Further, the ratio of the first to second moments of inertia of the current eccentric shaft is about 7.2 m−1 and requires excessive start-up torque to get the shaft rotating, thereby increasing operational costs and wear and tear on the motor that rotates the shaft. For example, the shaft 5 requires about 3.42 N·m over a 4 second start-up time period to get the shaft 5 rotating at a desired frequency of about 65 Hz. Reducing the start-up torque required could also produce substantial cost savings.
As a result, a need has therefore arisen to provide an improved eccentric shaft for a utility compactor lacking some or all the disadvantages described above.